As telecommunications technology progresses, a host of new broadband services can be provided over the public switched telecommunications networks, including broadcast television, cable television, interactive television, orders-on-demand, enhanced pay-per-view, etc. As would be understood, it is desirable that these broadband services along with traditional narrowband telephony services be delivered to the user in an efficient and economically feasible manner. One such network which delivers all of the above broadband and narrowband services uses hybrid fiber-coax technology, which takes advantage of the broadband capabilities of optical fiber and combines it with cost effective coaxial cable technology.
In general, a hybrid fiber-coax ("HFC") system is comprised of a central office/headend ("CO/HE"), a feeder system, a distribution system and a customer interface. The CO/HE establishes signaling and packet paths for all upstream and downstream communications. It is also the origination point for all downstream signals and as such, service provider signals are brought into the CO/HE, processed, combined, and converted to an optical format and sent over the feeder system to an optical node (or fiber node). The optical signal is then converted to an electrical signal in different radio frequencies ("RF") and sent over multiple coaxial cables to a network interface unit ("NIU") present on or near the subscriber's home. The NIU is an intelligent, addressable device which takes the combined RF electrical input and splits off the appropriate telephony and video signals to the home. In the reverse direction, upstream traffic originates from the NIU, where it is sent to the optical node. The optical node converts the signal from electrical to optical format and forwards it over the feeder system to the CO/HE.
HFC systems typically occupy up to the 750 MHz frequency bandwidth, where the available RF spectrum is allocated in accordance with the designated use of the system. A portion of that bandwidth is reserved for circuit-switched applications. The invention deals with the efficient utilization of this capacity.
In general, traffic is comprised of calls, each of which requires some number of time slots to carry a specified type of information (i.e., voice or video signals) over a designated RF channel. Voice information is carried over a Digital Service, level 0 ("DSO") channel, which has a rate of 64 kbps and video information is carried over an H-channel, specifically an H0 channel, which has a rate of 384 kbps. Bi-directional DSO service requests require a single time slot in the upstream and downstream directions and H0 service requests require four contiguous time slots in the upstream direction and six not necessarily contiguous time slots in the downstream direction. Since different service requests may interfere with each other, assignment of RF resources in the upstream and downstream directions have a significant impact on the resulting blocking probability.
In the upstream direction, calls must first obtain from the CO/HE a time slot on an RF frequency (as designated above) on the coaxial cable using a time division multiple access protocol. This upstream time slot assignment process is complicated by several factors. First, NIU transmitters are agile enough to dynamically change frequencies and so can access several different RF frequencies depending on the CO/HE. This capacity is shared by all the NIUs on the same coaxial cable and allows for significant concentration, which in turn means a possibility for blocking. Concentration is the process by which a potential offered load that exceeds the traffic-carrying capacity of the system is handled and blocking refers to an instance when a call cannot be handled by the network. As it takes time to change frequencies, an NIU transmitter can handle simultaneous calls on different frequencies only in certain non-overlapping time slots in the different accessible frequencies. As such, the assignment of time slots in the upstream direction is a dynamic process depending upon the available resources.
In the downstream direction, a call must also obtain a time slot on an RF frequency. However, in this direction, the NIU receiver is semi-permanently assigned to a particular frequency and thus at call setup time, only time slots within that frequency are available. NIUs that share a downstream frequency but are not necessarily on the same coax, are referred to as an NIU group. Since the assignments of NIU groups are semi-permanently defined, downstream assignments of frequency to an NIU can only be accomplished during idle times, i.e., when there are no calls on the NIU. As a result, downstream frequency assignments are not dynamic and require an evaluation process which considers the load carried by each NIU and each NIU group.
Accordingly, there is a need to provide a method and system which can dynamically assign upstream frequency channels and time slots and can automatically assign downstream frequency channels and time slots in view of the accepted load across all of the downstream frequencies.